Interlayers for laminated safety glass with superior de-airing and laminating properties and process for making the same

ABSTRACT

This invention relates to thermoplastic interlayers for laminated safety glass with superior vacuum de-airing at elevated temperatures and superior tacking and edge sealing properties. The sheeting has surface pattern on at least one of the surfaces characterized by flat surfaces with substantially uninterrupted channels for air flow in at least two intersecting directions. The channels allow for rapid de-airing while the area roughness parameter ratio AR p /AR t  in the range of 0.52 to 0.62, AR t  being less than 32 μm. and area kurtosis less than 2.5, allow for ease of tacking of the interlayer onto glass and edge sealing after de-airing has been completed. Said surface pattern may also be superimposed onto a pattern which is generated by melt fracture or other means on at least one side to enhance de-airing and aid edge sealing.

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/193,038, filed Mar. 29, 2000.

BACKGROUND OF THE INVENTION

[0002] In the fabrication of laminated safety glass, it is customary toplace a piece of thermoplastic sheeting between two pieces of floatglass. It is also common that the thermoplastic interlayer's surface canbe roughened to avoid blocking, i.e., one layer of interlayer stickingto another. The roughness on the interlayer can also allow theinterlayer to be moved while the two pieces of glass are aligned as theglass/interlayer/glass sandwich (hereinafter, “assembly”) isconstructed. In constructing such an assembly, air is trapped in theinterstitial space between the glass surface and the bulk of thethermoplastic interlayer. Trapped air can be removed either by vacuumde-airing or by nipping the assembly between a pair of rollers.

[0003] In the case of vacuum de-airing, air is removed while theassembly is at ambient temperature. Tacking of the interlayer to theglass and sealing of the edges is accomplished by heating the entireassembly while it is still under vacuum. The assembly, after the heatingstep, is generally referred to as a pre-press or a pre-laminate.

[0004] In the case of nipping, the assembly is generally heated to atemperature between 50-100° C., and is then passed through one or moresets of nip rolls. Edge sealing is accomplished by the force of therollers exerted on the two pieces of glass. At the end of the nippingstep, the assembly is called a pre-press. In windshield manufacture, thenip rolls are often articulated so as to accommodate the curvature inthe windshield. When complex shapes and angles are involved, or whenseveral models of windshields are made concurrently, it is often moreconvenient to use the vacuum de-airing method.

[0005] However, laminators may encounter a dilemma when selecting asuitable interlayer. It is sometimes difficult to choose an interlayerwith optimal features for pre-pressing, namely, rapid air removal andproper edge seal. Interlayers which have rougher surfaces as measured bythe 10-point roughness (ISO R468), Rz, can allow for faster de-airing.However, such interlayers can make it inconvenient to obtain edge sealas more energy is generally required to compact the rough interlayer. Ifthe edges of the pre-press are not completely sealed, air can penetratethe edge in the autoclaving step where the pre-press is heated underhigh pressure, and can cause visual defects in the laminate which iscommercially unacceptable. Laminators who use vacuum for de-airing inhot environments can have added difficulty. Interlayers that are roughand allow for rapid de-airing at about room temperature (23° C.) oftendo not de-air as well when the ambient temperature is much above 30° C.

[0006] On the other hand, relatively smooth interlayers can lead to theedges sealing before sufficient air is removed, and can leave airtrapped inside the pre-press. This problem is commonly referred to aspre-mature edge seal, and can be especially common with PVB interlayers.During autoclaving, the excess air may be forced into solution underhigh pressure, but may return to the gas phase after autoclaving.Defects which occur after lamination are often more costly to rectify.

[0007] The thermoplastic interlayers of this invention allow for rapidde-airing even at high temperatures, and also allow good edge seal to beobtained.

SUMMARY OF THE INVENTION

[0008] In one aspect the present invention is a glass/adhesive sheetlaminate comprising at least one layer of glass and a sheet of plasticinterlayer, said plastic interlayer having at least one surface embossedwith a pattern which provides relatively uninterrupted channels forde-airing in two intersecting directions, said channels having depthbetween 20 microns and 80 microns, and width 30 microns to 300 micronsand spaced between 0.1 mm and 1 mm apart.

DETAILED DESCRIPTION

[0009] Interlayers suitable for use in laminar structures comprising atleast one ply of glass such as plasticized PVB sheeting and otherthermoplastic interlayers are prepared by processes well known in theart. Preparation of plasticized PVB is disclosed in Phillips, U.S. Pat.No. 4,276,351 (Phillips), and by Hussey et al., WO 96/28504 (Hussey),for example. In Phillips, a compatible amount of tetraethylene glycoldiethylhexanoate is used in admixture with PVB to plasticize the resin.In Hussey, an adhesion control agent is used in addition to aplasticizer to make a PVB sheet. A wide variety of adhesion controlagents can be used with polyvinylbutyral sheeting. In the instantinvention a PVB sheet plasticized with a compatible quantity of glycolester selected from the group consisting of triethyleneglycoldi-n-heptanoate and tetraethylene glycol di-n-heptanoate, or with acompatible quantity of branched or unbranched di-esters such astriethylene glycol di-2-ethylbutyrate and triethylene glycoldi-2-ethylhexanoate, and contains as an adhesion control agent an alkalior alkaline earth metal carboxylate such as formate, acetate, and thelike, or a combination thereof. A process for preparing such sheeting isdisclosed in Moynihan, U.S. Pat. No. 4,292,372 (Moynihan). The teachingsof Moynihan can be useful in the practice of the present invention. InMoynihan a hydrolyzable ester is used as a plasticizer in conjunctionwith an adhesion control agent. Other suitable adhesion control agentsinclude, but are not limited to, potassium formate, potassium acetate,magnesium formate, magnesium acetate, magnesium neodecanoate, magnesiumsulfate, and calcium or zinc salts of various organic and inorganicacids.

[0010] The interlayer includes an adhesion control agent to provide apreselected level of adhesion between said layer of glass and saidinterlayer which is suitable for use as automobile windshields and sidewindows and body glass, as windows and windshields for vehicles oftransportation other than automobiles such as trains and buses, and asglazing material for buildings and architectural structures.

[0011] It is known that in order to effectively remove most of the airfrom between the surfaces in a PVB laminar structure, the surface of thePVB sheeting should be roughened. This can be effected by mechanicallyembossing or by melt fracture during extrusion of the PVB sheet followedby quenching so that the roughness is retained during handling.Retention of the surface roughness is essential in the practice of thepresent invention to facilitate effective removal of the entrapped airduring laminate preparation.

[0012] Surface roughness, Rz, can be expressed in microns by a 10-pointaverage roughness in accordance with ISO-R468 of the InternationalOrganization for Standardization and ASME B46.1 of the American Societyof Mechanical Engineers. For sheeting having a thickness greater thanabout 0.76 mm, 10-point average roughness, Rz, of up to 80 μm issufficient to prevent air entrapment. To prevent blocking a minimumroughness of about 20 μm is needed if the sheeting is to be wound up ina roll without interleaving or without anti-blocking agents. Channels onthe surface to provide roughness have a depth of from about 20 to about80 μm, preferably from about 25 to about 70 μm, more preferably fromabout 30 to about 60 μm. The width of the channels is from about 30 μmto about 300 μm, preferably from about 40 to about 250 μm, and morepreferably from about 50 to about 200 μm. The surface channels arespaced between from about 0.1 mm to about 1 mm apart, preferably fromabout 0.1 to about 0.9 mm apart, more preferably from about 0.15 toabout 0.85 mm apart.

[0013] Surface roughness, Rz, measurements from single-traceprofilometer measurements can be adequate in characterizing the averagepeak height of a surface with roughness peaks and valleys that arenearly randomly distributed. However a single trace profilometer may notbe sufficient to characterize the texture of a surface that has certainregularities, especially straight lines. In characterizing suchsurfaces, if care is taken such that the stylus of the surface textureinstrument does not ride in a groove or on a plateau, the Rz thusobtained can still be a valid indication of the surface roughness. Othersurface parameters, such as the mean spacing (R Sm) may not be accuratebecause they depend on the actual path traversed. Parameters like R Smcan change depending on the angle the traversed path makes with thegrooves. Surfaces with regularities like straight-line grooves arebetter characterized by three-dimensional or area roughness parameterssuch as the area peak height, AR_(p), and the total area roughness,AR_(t), and the area kurtosis as defined in ASME B46.1. AR_(p) is thedistance between the highest point in the roughness profile over an areato the plane if all the material constituting the roughness is melteddown. AR_(t) is the difference in elevation between the highest peak andthe lowest valley in the roughness profile over the area measured. Inthe instant invention, the surface pattern of the interlayer ischaracterized by AR_(t) less than 32 μm, and the ratio of AR_(p) toAR_(t), also defined in ASME B46.1-1, is between 0.42 and 0.62,preferably 0.52 to 0.62. Said interlayer also has area roughnesskurtosis less than 2.5.

[0014] A pre-press, as described hereinabove, can be measured for haze,and the haze values averaged. A pre-press having average haze of lessthan about 70% is preferable. A pre-press having average haze of lessthan about 50% is more preferred. A pre-press having average haze ofless than about 20% is most preferred.

EXAMPLES

[0015] The following Examples and Comparative Examples are intended tobe illustrative of the present invention, and are not intended in anyway to limit the scope of the present invention.

[0016] In some of the examples of this invention, 100 parts of dry PVBflake of nominally 23% by weight of unbutyralated vinyl alcohol groupswere mixed with 38-40 parts of tetraethylene glycol di-n-heptanoateplasticizer and one or more light stabilizers marketed under thetradename “Tinuvin” by Ciba-Geigy Co. and an antioxidant which werepre-mixed in the plasticizer continuously in a twin-screw extruder. Themelt was forced through a slot die and formed a sheeting of 0.76 mmnominal thickness. In addition, agents for modifying surface energy ofthe bulk interlayer and usual adjuvants such as antioxidants, colorantsand ultraviolet absorbers which do not adversely affect the functioningof the surface energy modifying agent and adhesion control agent can beincluded in the PVB composition. Commercially available interlayers suchas Butacite® plasticized polyvinylbutyral resin sheeting available fromthe DuPont Company are used as starting materials in some of theexamples.

[0017] Surface Roughness Characterization

[0018] Surface roughness, Rz, can be expressed in microns by a 10-pointaverage roughness in accordance with ISO-R468 of the InternationalOrganization for Standardization. Roughness measurements are made usinga stylus-type profilometer (Surfcom 1500A manufactured by Tokyo SeimitsuKabushiki Kaisha of Tokyo, Japan) as described in ASME B46.1-1995 usinga trace length of 26 mm. AR_(p) and AR_(t), and the area kurtosis aremeasured by tracing the roughness over a 5.6 mm×5.6 mm area in 201 stepsusing the Perthometer Concept system manufactured by Mahr GmbH,Gottingen, Germany.

[0019] De-Airing Efficiency at Room Temperature

[0020] De-airing efficiency of an interlayer with a specified pattern isdetermined using an apparatus which allows the absolute pressure of theinterstitial space in an assembly to be measured. The interlayer to betested is assembled as a normal assembly, except that the top plate ofglass has a hole drilled through its center. The glass, the interlayer,and all auxiliary equipment must be equilibrated to 22.5±2.5° C. for onehour before testing. If an interlayer has two distinctly differentpatterns on either side, the side with the surface pattern to beevaluated is placed in contact with the piece of glass with a hole. Thebase of a pressure (or vacuum) coupler is affixed and sealed around thehole in the glass (a vacuum coupler is a device which, when connected,enables air to move between an enclosure and the outside). A piece offabric (about 30 mm wide) is wrapped around the edges of the assembly.The base of another vacuum coupler plate is placed on top of two layersof cotton fabric (50 mm×50 mm) in one of the corners. The assembly withthe peripheral breather and two base plates of couplers are then placedinside a 0.1-mm thick nylon bag. The bag is then heat-sealed.Cross-marks are cut through the bag just above the base plates. Vacuumcouplers are attached through the nylon bag and care is taken to ensurethat there are no leaks, as shown in FIG. 1. The corner plate isattached to the vacuum source (nominally 84 kPa below atmospheric),while the center plate is attached to a vacuum gauge or a calibratedpressure transducer. The gauge reading (or transducer output) isrecorded at given intervals after the vacuum is applied. The recordeddata contain the absolute interstitial pressure at 10-second intervalsfor the first minute after vacuum is applied, at 15-second intervalsthereafter for one-half minute, at 30-second intervals thereafter foranother one-half minute, and at one-minute intervals thereafter up to 10minutes after the application of vacuum. A surface that allows forefficient vacuum de-airing would cause the absolute interstitialpressure to drop rapidly within a few minutes. The interstitial pressureat 90 seconds after evacuation is indicative of how well the interlayerde-airs. If at 90 seconds after evacuation, the absolute interstitialpressure is above 53.3 kPa, de-airing is inadequate, and the interlayeris not suitable for vacuum de-airing.

[0021] De-Airing Efficiency at Elevated Ambient Temperature

[0022] Determination of de-airing efficiency at high (elevated) ambienttemperature is the same as that at room temperature, except that theinterlayer to be tested, the glass, couplers are all equilibrated to30.5±2.5° C. prior to testing. If at 90 seconds after evacuation, theabsolute interstitial pressure is above 53.3 kPa, de-airing isinadequate, and the interlayer is not suitable for vacuum de-airing whenthe ambient temperature is elevated, as in the summer.

[0023] Pre-Press Haze Measurement

[0024] A pre-press is made from each PVB interlayer tested. The TAATglass orientation is used. A PVB interlayer is placed between two piecesof glass, the excess interlayer is trimmed. The glass/PVB/glasssandwich, referred to as an assembly, is placed in a 0.1-mm (nylon)plastic bag. A vacuum adapter allows a vacuum hose to be connected tothe inside of the plastic bag after it is sealed. The bag with theassembly inside is evacuated for 90 seconds at 53.3 kPa vacuum (48.0 kPaabsolute pressure) at ambient temperature (22.5° C.±2.5° C.). After theinitial vacuum, the nylon bag and its contents and the vacuum hose isplaced inside an oven kept at 120-122° C. for 6 minutes. Vacuum issupplied from a vacuum pump via a hose that runs through the oven sothat there is no interruption in the vacuum as the assembly is placedinto the oven. At the end of the six minutes in the oven, the nylon bagis removed from the oven and the vacuum hose is disconnectedimmediately. The glass/PVB/glass structure at this stage is called apre-press. Depending on the starting interlayer roughness, the pre-pressmay appear hazy or clear. Haze is measured by using a Hazegard hazemeterfrom Gardner in eight places in the pre-press. The results can beaveraged.

Comparative Example C1

[0025] Polyvinyl butyral (PVB) interlayer available commercially from E.I. DuPont de Nemours & Co. as Butacite® B-142 was characterized. Surfaceroughness was generated by melt fracture. The roughness parameters ofthe surface pattern are shown in Table 1. The de-airing characteristicsat room temperature and at elevated ambient temperature were determinedin the tests outlined above. Separately, a pre-press was prepared usingthe conditions specified above. Results are shown in Table 1.

Comparative Example C2.

[0026] PVB interlayer available commercially from E. I. DuPont deNemours & Co. as Butacite® BE-1990 was characterized. Surface roughnesswas generated by melt fracture. Its roughness parameters are shown inTable 1. Its de-airing characteristics at room temperature and atelevated ambient temperature were determined in the tests outlinedabove. Separately, a pre-press was prepared using the conditionsspecified above. Results are shown in Table 1.

Example 1

[0027] The interlayer from Comparative Example C1 was placed between tworubber plates. The rubber surfaces in contact with the PVB interlayerwere engraved with a pattern with ridges that form a grid pattern. Theridges were approximately 12 μm in width and 45 μm in height, and werespaced such that there were approximately 9 grids per square mm. Therubber/PVB/rubber sandwich assembly was placed between two pieces ofnominally 3.2-mm thick annealed glass. The 5-ply sandwich was put insideof a woven nylon bag, and the nylon bag and its contents were placedinside of a rubber vacuum bag. The rubber vacuum bag was fitted with apiece of tubing which was sealed through the edge of the bag, and whichenabled connection to a vacuum source. The open end of the vacuum bagwas closed. Vacuum (at least 80 kPa below atmospheric) at ambienttemperature (22.5±2.5° C.) was applied for 5 minutes. Immediatelythereafter, the vacuum bag with its contents was placed in an oven at120° C. for 40 minutes. After that time, the vacuum bag was removed fromthe oven. Vacuum was disconnected, and the vacuum bag and its contentswere allowed to cool to room temperature. One of the engraved rubberplates was gently removed to expose the now embossed PVB interlayer. ThePVB interlayer was then gently peeled off from the second embossedrubber plate. The embossed pattern on the PVB interlayer was grid-likewith channels approximately 12 μm wide and 41 μm deep, and withapproximately 9 grids per square mm. The roughness parameters are shownin Table 1. The de-airing performance at room temperature and elevatedambient temperature, and pre-pressing characteristics are shown in Table1.

Comparative Example C3

[0028] 100 Parts by weight polyvinyl butyral are mixed in an extruderwith 38.5 parts of tetraethylene glycol di-heptanoate plasticizer dopedwith antioxidants (octylphenol) and ultraviolet light stabilizer(Tinuvin P, Ciba Geigy). The admixture was forced through a slit-die sothat it becomes a nominally 0.76 mm sheeting. Agents for controllingadhesion to glass and surface tension of the bulk interlayers were addedin quantities to make the interlayer suitable for use in automobiles.Immediately exiting the die, the molten plasticized PVB sheet wascalendered between a quench drum and an embossing roll made of siliconerubber. The surface of the quench drum was sandblasted and transferred arandom pattern with an Rz of approximately 30 μm onto the PVBinterlayer. The embossing roll was engraved with a pattern similar tothat on the quench drum. Roughness parameters for the rubber-embossedsurface are shown in Table 1. The de-airing performance of therubber-embossed surface at room temperature and elevated ambienttemperature are also shown in Table 1, as is the haze of the pre-pressfrom this interlayer.

Example 2

[0029] The interlayer used in this example was prepared in the same wayas that in Comparative Example C3 except that the rubber embossing rollwas engraved with a pattern like those on the rubber sheets used inExample 1. One side of this interlayer had the regular grid-like patternfrom the rubber-embossing roll while the other side had the random,sandblasted pattern from the quench drum. The roughness, Rz, of therubber embossed surface of this PVB interlayer was about 40 μm. Thede-airing performance of the rubber-embossed surface at room temperatureand elevated ambient temperature are shown in Table 1 as is the haze ofthe pre-press from this interlayer. TABLE 1 Elevated⁺ Pre- Ratio RoomAmbient Press Rz AR_(t) AR_(p) AR_(p) Area Temperature Temperature HazeExample (μm) (μm) (μm) AR_(t) Kurtosis De-Airing* De-Airing (%) C1 41.854.17 35.87 0.662 3.46 42.3 64.2 49.2 C2 62.6 74.99 48.14 0.642 3.1236.9 61.0 62.3 1 39.6 48.32 29.33 0.607 1.78 16.2 16.5 11.7 C3 49.066.03 44.95 0.681 1.92 49.1 73.4 24.5 2 39.2 47.90 28.70 0.599 1.93 16.924.0 13.3

1. A glass/adhesive sheet laminate comprising at least one layer ofglass and a sheet of plastic interlayer, said plastic interlayer havingat least one surface with a pattern which provides relativelyuninterrupted channels for de-airing in at least two intersectingdirections, said channels having depth between 20 μm and 80 μm, andwidth 30 μm to 300 μm and spaced between 0.1 mm and 1 mm apart.
 2. Aplastic interlayer as in claim 1 having roughness parameters such thatthe area roughness peak height, AR_(p), is less than 32 μm, and theratio of the of AR_(p) to AR_(t) is between 0.52 and 0.62, and the areakurtosis is less than 2.5.
 3. The laminar structure of claim 1 whereinsaid interlayer is an ionomeric polymer.
 4. The laminar structure ofclaim 1 wherein said interlayer is a PVB sheeting plasticized with oneor more glycol-di-ester plasticizers and contains suitable amounts ofadhesion control additive and surface active agents.
 5. The laminarstructure of claim 3 wherein said adhesion control agent is a potassiumor an alkali earth metal salt of an organic acid or inorganic acid, or acombination thereof.
 6. A process for imparting the surface pattern ontothe interlayer in claim 1 where the pattern is transferred via embossingan interlayer material with an existing pattern.
 7. A process forimparting the surface pattern onto the interlayer in claim 1 whereby themolten interlayer is calendered between embossing rolls, at least one ofthe rolls is engraved with the pattern described in claim 1.